1. Field of the Invention
The present invention relates to a chalcopyrite structure semiconductor thin film containing a specific dopant and a process of producing the same.
2. Description of the Related Art
The chalcopyrite structure semiconductor is a material useful for constituting light-emitting devices and solar cells, because its forbidden band can be wide from a visual region to an infrared ray region and it has a large optical absorption coefficient due to the constituent elements. It is indispensable to produce a p-n junction in manufacturing the solar cells or light-emitting devices. For controlling a p-n conduction type of the chalcopyrite thin film, a method of changing the composition ratio between a Group I element and a Group III element or between a Group II element and a Group IV element which are the constituent elements of chalcopyrite compounds has been used conventionally. For example, in the case of CuInSe.sub.2 thin film, n-type is formed when the proportion of the Group III element Cu is less than that of the Group I element In, and in the opposite case p-type is formed. In these cases, such problem is encountered that many lattice defects occur due to deviations in the composition ratio. There are also such problems as depositions of excessive components or appearance of an impurity phase other than the chalcopyrite structure. R. Noufi et al., also report that, it is difficult to control a carrier concentration and resistivity by changing the composition ratio (Appl. Phys. Lett., 45 (1984) p. 688). Particularly, most of the chalcopyrite semiconductor thin film which takes the n-type by deviation in the composition ratio shows a high resistance, and thus a low resistance film is not obtainable.
In fabricating the p-n Junction by using the chalcopyrite thin film produced by the prior art, such inconvenience as the lattice defects and depositions of excessive components owing to deviations of composition ratio, or the impurity phase other than the chalcopyrite-structure appears as mentioned before. Thereby, electrical and optical characteristics of the chalcopyrite thin film are deteriorated. Thus, when the devices having the p-n junction are manufactured by using the chalcopyrite thin film produced by the prior art, efficiency of the devices are inferior due to the deterioration of electrical and optical characteristics. For example, by increase of carrier recoupling centers due to the lattice defects and the impurity phase, an open-circuit voltage of the solar cell drops and also a quantum efficiency of semiconductor laser drops.
When an n-type high resistance film is used, in the solar cells a short-circuit current decreases, and in the light-emitting devices a carrier injection efficiency reduces. Thus, a conversion efficiency of the solar cells and a luminous efficiency of the light-emitting devices are deteriorated.
Moreover, in the solar cells, a depletion layer of the p-n Junction must be broaden to convert incident light efficiently into electrical energy. Thus it is necessary to control the carrier concentration.